I DS on ebay from a franchise in the states with an online catalog. I have competitors selling from the same supplier, except they sell at prices that would always leave them negative profit...even if they were a TRS.

could be the website owner is selling ,or a relative/kid/family member who has access to the warehouse and buy at wholesale price or at a discount to your price.
or an employee who can buy at a discount .
if your cost is $10,their cost is anywhere between $4.50 - $7.
what you need to do is find his supplier and buy in volume